Capacitance detection device and capacitance detection method

ABSTRACT

A capacitance detection device includes at least one detection electrode, a shield electrode disposed in close vicinity of the detection electrode, an AC signal source that supplies an AC signal to the shield electrode, a detection circuit that detects capacitance between a physical object in close vicinity of the detection electrode and the detection electrode on the basis of a detection signal output from the detection electrode and the AC signal output from the AC signal source, and a phase adjustment circuit provided between the AC signal source and the shield electrode. The phase adjustment circuit advances the phase of the AC signal output from the AC signal source.

CLAIM OF PRIORITY

This application is a Continuation of International Application No.PCT/JP2021/019641 filed on May 24, 2021, which claims benefit ofJapanese Patent Application No. 2020-139645 filed on Aug. 20, 2020. Theentire contents of each application noted above are hereby incorporatedby reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a capacitance detection device and acapacitance detection method.

2. Description of the Related Art

An impedance detection circuit has been developed that is capable ofoutputting a signal proportional to the capacitance to be measured. Theimpedance detection circuit includes an AC signal generator thatgenerates an AC signal, an operational amplifier including an invertinginput terminal, a non-inverting input terminal, and an output terminal,where the output terminal and the inverting input terminal are connectedby a feedback resistor and where the AC signal is applied to thenon-inverting input terminal, a signal line having one end connected tothe inverting input terminal, where the capacitance to be measured canbe connected to the other end, a shield line that allows the signal lineto be partially exposed and that is connected to the non-inverting inputterminal, and a compensation circuit that receives the AC signal andcompensates the phase and amplitude of the AC signal, where the outputof the compensation circuit is connected to the inverting input terminalof the operational amplifier (refer to, for example, Japanese UnexaminedPatent Application Publication No. 2002-350477).

In existing impedance detection circuits, phase compensation isperformed so that the phase delay of the input to the inverting inputterminal caused by the parasitic capacitance of the signal line and thefeedback resistance do not affect the phase of the output of theoperational amplifier. However, since the phase of the input to theinverting input terminal of the operational amplifier remains unchanged,a phase difference occurs between the input to the inverting inputterminal and the input to the non-inverting input terminal of theoperational amplifier. For this reason, even if the output of thecompensation circuit is input to the inverting input terminal, the phasedelay of the input of the capacitance to be detected to the invertinginput terminal with respect to the phase of the input to thenon-inverting input terminal does not disappear. The reason is asfollows: An interconnection wire from the capacitance to be detected tothe inverting input terminal has a resistance value, and the input to bedetected needs to be taken out as a current. At this time, a potentialdifference occurs between the voltage of the non-inverting inputterminal and the voltage of an electrode of the capacitance. In such acompensation technique, if, in particular, the resistance of theinterconnection wire between a detection target and the inverting inputterminal is high or if the parasitic capacitance existing in theinterconnection wire is large, the phase delay of the input current tobe detected due to the influence of the resistance value is notsubstantially corrected. As a result, the output sensitivity (thedetection sensitivity) of the operational amplifier is decreased.

SUMMARY OF THE INVENTION

The present invention provides a capacitance detection device and acapacitance detection method capable of reducing a decrease in detectionsensitivity due to a signal phase delay.

According to an embodiment of the present invention, a capacitancedetection device includes at least one detection electrode, a shieldelectrode disposed in close vicinity of the detection electrode, an ACsignal source that supplies an AC signal to the shield electrode, adetection circuit that detects capacitance between a physical object inclose vicinity of the detection electrode and the detection electrode ona basis of a detection signal output from the detection electrode andthe AC signal output from the AC signal source, and a phase adjustmentcircuit provided between the AC signal source and the shield electrode.The phase adjustment circuit advances the phase of the AC signal outputfrom the AC signal source.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a capacitance detection device according to anembodiment;

FIG. 2 illustrates the configuration of a detection circuit;

FIG. 3 illustrates simulation results of the phase/gain—frequencycharacteristics of an output signal with respect to an input signal of aphase shift circuit;

FIGS. 4A to 4D illustrate the phase relationship among signals obtainedbetween an AC signal source and a detection electrode;

FIGS. 5A and 5B illustrate the resistance and capacitance in the sensorunit of the capacitance detection device;

FIG. 6 illustrates signal waveforms in units of the capacitancedetection device;

FIG. 7 illustrates a differential amplifier;

FIG. 8 illustrates a capacitance detection device according to amodification of the embodiment;

FIGS. 9A to 9C illustrate the signal waveforms in units of thecapacitance detection device; and

FIG. 10 is a diagram describing a phase adjustment amount in a phaseadjustment circuit of the capacitance detection device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments to which a capacitance detection device and a capacitancedetection method according to the present invention are applied aredescribed below.

EMBODIMENTS

FIG. 1 illustrates a capacitance detection device 100 according to theembodiment. The capacitance detection device 100 includes a sensor unit110, an AC signal source 120, a detection circuit 130, and a phaseadjustment circuit 140. The capacitance detection method is a method foradjusting a phase (described below) to detect the capacitance by usingthe capacitance detection device 100.

Hereinafter, the sensor unit 110 is described by defining an XYZcoordinate system. In addition, for convenience of description, in thesensor unit 110, the -Z direction side is referred to as the lower sideor the bottom, and the +Z direction side is referred to as the upperside or the top. However, this does not represent a universal verticalrelationship. Furthermore, in terms of the sensor unit 110, XY-planeview is referred to as plan view.

The sensor unit 110 includes, for example, 12 detection electrodes 111and one active shield electrode 112. The 12 detection electrodes 111 arearranged in a matrix of 3 rows×4 columns. The detection electrode 111 isan electrode that detects the capacitance between the detectionelectrode 111 and the human body (typically the hand) by aself-capacitance method. For example, the detection electrode 111 ismade of a conductive material, such as IOT (indium Tin Oxide) film, witha sheet resistance of several 10 Ω/

to about 100Ω/

. This is the level that causes an effect of reducing the sensitivity inthe existing technique. The human body, such as the hand, is an exampleof a physical object that is a detection target of the capacitancedetection device 100.

Note that an ITO film or the like serving as a conductive materialprovides such a large time constant that if the phase adjustment circuit140 (described below) does not adjust the phase of an AC signal appliedto the active shield electrode 112, phase delay that decreases thedetection sensitivity of the detection circuit 130 occurs in the ACsignal propagating in the detection electrode 111. For example, thedetection electrode 111 is formed on a surface of the transparentsubstrate. The material of the detection electrode 111 is not limited toITO and may be zinc oxide, tin oxide, titanium oxide, or the like. Inaddition, the detection electrode 111 need not be transparent.

The active shield electrode 112 is disposed at a position so as tooverlap the 12 detection electrodes 111 in plan view and is providedunder (at the back side of) the 12 detection electrodes 111. Inaddition, an AC signal source 120 is connected to the active shieldelectrode 112 via a phase adjustment circuit 140. The active shieldelectrode 112 is provided to shield the 12 detection electrodes 111 fromnoise and to reduce parasitic capacitance. An AC signal that is outputfrom the AC signal source 120 and that has a phase advanced by the phaseadjustment circuit 140 is applied to the active shield electrode 112.

For example, the active shield electrode 112 is made of a conductivematerial, such as an ITO film. The effect of phase delay due to the useof the ITO film for the active shield electrode 112 is the same as thatfor the detection electrode 111, and the effect is that the activeshield electrode 112 has a resistance value that causes such a largetime constant that the phase delay that decreases the detectionsensitivity of the detection circuit 130 occurs in an AC signalpropagating through the active shield electrode 112 if the phaseadjustment circuit 140 (described below) does not adjust the phase ofthe AC signal applied to the active shield electrode 112.

The active shield electrode 112 is disposed in close proximity to the 12detection electrodes 111. The active shield electrode 112 in closeproximity to the 12 detection electrodes 111 means the active shieldelectrode 112 located close to the 12 detection electrodes 111 so thatthe active shield electrode 112 can shield the 12 detection electrodes111 mainly from noise coming from below and reduce parasitic capacitancedue to the coupling with parts around and below the active shieldelectrode 112. Note that the material of the active shield electrode 112is not limited to ITO and may be zinc oxide, tin oxide, titanium oxide,or the like. In addition, the active shield electrode 112 need not betransparent.

The AC signal source 120 supplies an AC signal to the active shieldelectrode 112. More specifically, the AC signal source 120 includes anoutput terminal connected to the input terminal of phase adjustmentcircuit 140 and outputs an AC signal to the phase adjustment circuit140. The AC signal output from the AC signal source 120 is supplied tothe active shield electrode 112 with its phase advanced by the phaseadjustment circuit 140. The frequency of the AC signal is, for example,30 kHz to 300 kHz.

The detection circuit 130 detects the capacitance between a physicalobject in close proximity to the detection electrode 111 and thedetection electrode 111 on the basis of the detection signal output fromthe detection electrode 111 and the AC signal output from the AC signalsource 120. More specifically, the detection circuit 130 includes 12input terminals 130A, one input terminal 130B, and 12 output terminals130C. The 12 input terminals 130A are connected to the 12 detectionelectrodes 111 in a one-to-one manner. The input terminal 130B isconnected to the output terminal of the AC signal source 120. The 12output terminals 130C are connected to an electronic device includingthe capacitance detection device 100, an electronic device disposedoutside the capacitance detection device 100, or the like. Theelectronic device may be any electronic device that uses the capacitancedetection device 100 as an input device. Examples of the electronicdevice includes a smartphone, a tablet, and a copying machine.

The detection circuit 130 is described below with reference to FIG. 2 .FIG. 2 illustrates the configuration of the detection circuit 130. Thedetails of circuits that physically configure the detection circuit 130are not illustrated. The detection circuit 130 includes a multiplier 131and a low pass filter (LPF) 132. The detection circuit 130 includes 12multipliers 131 and 12 LPFs 132. Note that FIG. 2 illustrates only onemultiplier 131 and only one LPF 132.

The input terminal 130A is connected to one of two input terminals ofthe multiplier 131, and the input terminal 130B is connected to theother input terminal. An output terminal of the multiplier 131 isconnected to an input terminal of the LPF 132. An input signal inputfrom the detection electrode 111 to the input terminal 130A is a signalobtained by superimposing an AC signal propagating from the activeshield electrode 112 on a signal obtained from the capacitance betweenthe detection electrode 111 and the physical object, such as the hand.An input signal input to the input terminal 130B is the AC signal outputfrom the AC signal source 120.

The input signal input to the input terminal 130A is a signal generatedas follows: the phase of the AC signal output from the AC signal source120 is advanced by the phase adjustment circuit 140, the phase isdelayed when the AC signal propagates through the active shieldelectrode 112 and the detection electrode 111, and a signal based on acapacitance with a physical object, such as the hand, is superimposed onthe AC signal. The phase adjustment circuit 140 advances the phase ofthe AC signal output from AC signal source 120 so that the phase of theinput signal input to the input terminal 130A is the same as the phaseof the input signal input to the input terminal 130B and outputs the ACsignal to the active shield electrode 112. Therefore, the phase of theinput signal input to the input terminal 130A is the same as the phaseof the input signal input to the input terminal 130B, and the signalshaving the same phase are input to the two input terminals of themultiplier 131.

When the signals that are the same are input to the two input terminalsof the multiplier 131 and are multiplied, a signal having a frequencydoubled and superimposed on the direct current (DC) component isobtained, and the obtained signal is input from the output terminal ofthe multiplier 131 to the LPF 132. The LPF 132 allows band componentsbelow a predetermined cutoff frequency of the output of the multiplier131 to pass therethrough and outputs the band components from the outputterminal 130C. The output of the LPF 132 is a DC component correspondingto the signal obtained based on the capacitance between detectionelectrode 111 and the physical object, such as the hand.

The phase adjustment circuit 140 is provided between the AC signalsource 120 and the active shield electrode 112 and advances the phase ofthe AC signal output from the AC signal source 120. In particular, thephase adjustment circuit 140 advances the phase of the AC signal so thatthe detection signal input to the detection circuit 130 and the ACsignal are in phase. More specifically, the phase adjustment circuit 140includes a phase shift circuit 140A and an inverting amplifier circuit140B. The phase shift circuit 140A includes an operational amplifier141A, a variable capacitor 142A, a variable resistor 143A, and resistors144A and 145A. The inverting input terminal and the non-inverting inputterminal of the operational amplifier 141A are connected to the outputterminal of the AC signal source 120 via the resistor 144A and thevariable resistor 143A, respectively. The resistor 145A serving as afeedback resistor is connected between the inverting input terminal andthe output terminal of the operational amplifier 141A. The resistancevalues of the resistors 144A and 145A are both Ra. One end of thevariable capacitor 142A is connected between the non-inverting inputterminal of the operational amplifier 141A and the variable resistor143A. The other end of the variable capacitor 142A is connected toground. The output terminal of the operational amplifier 141A isconnected to the input terminal of the inverting amplifier circuit 140B.

The phase shift circuit 140A can variably control the input voltage ofthe non-inverting input terminal of the operational amplifier 141A bychanging a capacitance Cs of the variable capacitor 142A and theresistance value Rs of the variable resistor 143A. That is, the phaseshift circuit 140A delays the phase of the AC signal output from theoutput terminal of the operational amplifier 141A relative to the ACsignal input to the inverting input terminal by controlling the inputvoltage of the non-inverting input terminal of the operational amplifier141A.

The inverting amplifier circuit 140B includes an operational amplifier141B and resistors 142B and 143B. The non-inverting input terminal ofthe operational amplifier 141B is connected to ground, and the invertinginput terminal of the operational amplifier 141B is connected to theoutput terminal of the operational amplifier 141A of the phase shiftcircuit 140A via the resistor 142B. An output terminal of theoperational amplifier 141B is connected to the active shield electrode112. The resistor 143B serving as a feedback resistor is connectedbetween the inverting input terminal and the output terminal of theoperational amplifier 141B. The resistance values of the resistors 142Band 143B are both Rb. The inverting amplifier circuit 140B inverts thephase of the AC signal input to the inverting input terminal of theoperational amplifier 141B (shifts the phase by 180 degrees) and outputsthe AC signal.

Herein, the amount of phase delay that occurs in the AC signal due tothe time constant of the active shield electrode 112 and detectionelectrode 111 and the interconnection wires or the like connected to theactive shield electrode 112 and the detection electrode 111 is definedas α degrees. The phase adjustment circuit 140 delays the phase of theAC signal input from AC signal source 120 by (π−α) degrees by using thephase shift circuit 140A, inverts the phase by using inverting amplifiercircuit 140B, and outputs the AC signal. Thus, the phase of the ACsignal output from the phase adjustment circuit 140 leads the phase ofthe AC signal input to the phase adjustment circuit 140 by α degrees.The capacitance Cs and resistance Rs can be determined such that after α(degrees) is measured by experiments or simulations, a delay of αdegrees is achieved using a time constant RsCs determined by thecapacitance Cs of the variable capacitor 142A of the phase shift circuit140A and the resistance value Rs of the variable resistor 143A.

FIG. 3 illustrates the simulation results of frequency characteristicsof the phase and gain of the output signal with respect to the inputsignal of the phase shift circuit 140A. In FIG. 3 , the abscissarepresents frequency f, and the frequency at which the phase shift is−90 degrees is fd=1/(2πRsCs) (Hz). The frequency fd on the abscissa isthe frequency determined by the time constant RsCs determined by thecapacitance Cs of the variable capacitor 142A of the phase shift circuit140A and the resistance value Rs of the variable resistor 143A. Theordinate in FIG. 3 represents the phase and the gain of the outputsignal of the phase shift circuit 140A. The phase is denoted by a dashedline, and the gain is denoted by a solid line.

As illustrated in FIG. 3 , the phase continuously changes from 0 degrees(phase shift of 0 degrees) to −180 degrees (phase shift of −180degrees). Even when the frequency f changes, the gain is 0 dB. As can beseen from the above, the phase shift circuit 140A can shift the phase ofthe output signal with respect to the input signal from 0 degrees to−180 degrees, and the signal levels of the input signal and the outputsignal do not change.

When the phase of the output signal of the phase shift circuit 140Ahaving such a configuration is inverted by the inverting amplifiercircuit 140B, the phase of the output signal of the inverting amplifiercircuit 140B is shifted from −180 degrees to −360 degrees with respectto the phase of the input signal of the phase shift circuit 140A. Thatis, the phase adjustment circuit 140 can advance the phase of the inputsignal of the phase shift circuit 140A by 0 degrees to 180 degrees.

FIGS. 4A to 4D illustrate the phase relationship of signals obtainedbetween the AC signal source 120 and the detection electrode 111. FIG.4A illustrates the phase of the output signal of the detection electrode111 when the phase adjustment amount in the phase adjustment circuit 140is 0 degrees. FIG. 4B illustrates the phase of the AC signal of the ACsignal source 120. FIG. 4C illustrates the phase of the output signal ofthe phase shift circuit 140A. FIG. 4D illustrates the phase of theoutput signal of the inverting amplifier circuit 140B.

When the phase of the AC signal of the AC signal source 120 illustratedin FIG. 4B is used as a reference, the phase of the output signal of thedetection electrode 111 illustrated in FIG. 4A when the adjustmentamount in the phase adjustment circuit 140 is 0 degrees is delayed by αdegrees. In addition, as illustrated in FIG. 4C, the phase of the outputsignal of the phase shift circuit 140A is delayed by (π−α) degrees withrespect to the phase of the AC signal of the AC signal source 120illustrated in FIG. 4B. The phase of the output signal of the invertingamplifier circuit 140B illustrated in FIG. 4D leads the phase of the ACsignal of the AC signal source 120 illustrated in FIG. 4B by a degrees.As illustrated in FIG. 4D, if an AC signal having a phase advanced withrespect to the AC signal of the AC signal source 120 by α degrees isinput to the active shield electrode 112, the AC signals input to thetwo input terminals of the multiplier 131 of the detection circuit 130can be in phase.

FIGS. 5A and 5B is a schematic illustration of the resistance andcapacitance of the sensor unit 110 of the capacitance detection device100. FIG. 5A illustrates a portion of the sensor unit 110 and a portionof the active shield electrode 112 corresponding to one of the detectionelectrodes 111. The detection electrode 111 is illustrated as a resistorR111, and the active shield electrode 112 is illustrated as resistorsR112. In addition, the capacitance generated in a gap between thedetection electrode 111 and the active shield electrode 112 isillustrated as a capacitor CG, the capacitance between the hand H andthe detection electrodes 111 is illustrated as a capacitor CH, and theparasitic capacitance of the detection electrodes 111 is illustrated asa capacitor CP.

The AC signal input to the active shield electrode 112 flows to thedetection electrode 111 via the capacitor CG. Since the sensor unit 110has the resistors R111 and R112 as resistance values and has thecapacitors CG, CH, and CP, there is a time constant based on theresistance values of the resistors R111 and R112 and the capacitancevalues of the capacitors CG, CH, and CP. The time constant causes phasedelay of the AC signal output from the detection electrode 111 withrespect to the AC signal input to the active shield electrode 112.

In FIG. 5B, as indicated by (2), the phase of the output signal of thephase adjustment circuit 140 leads the phase of the AC signal of the ACsignal source 120 indicated by (1) by α degrees. If the AC signal whosephase is advanced with respect to the AC signal of the AC signal source120 by α degrees is input to the active shield electrode 112, the phaseof the output signal of the detection electrode 111 is delayed withrespect to the AC signal input to the active shield electrode 112 by αdegrees as indicated by (3). Therefore, the output signal of thedetection electrode 111 and the AC signal of the AC signal source 120indicated by (1) are in phase. Thus, two AC signals having the samephase can be input to the two input terminals of the multiplier 131.

FIG. 6 illustrates the signal waveform of each of elements of thecapacitance detection device 100. FIG. 6 illustrates (1) the AC signalof the AC signal source 120; (2) the output signal of the detectionelectrode 111; (3) the output signal of the multiplier 131; and (4) theoutput signal of the LPF 132. In terms of (2) the output signal of thedetection electrode 111 and (4) the output signal of the LPF 132, thesignal waveform when the phase is adjusted by the phase adjustmentcircuit 140 is denoted by a solid line, and the signal waveform when thephase is not adjusted by the phase adjustment circuit 140 is denoted bya dashed line.

When the phase is adjusted by the phase adjustment circuit 140, thephases of the AC signal of the AC signal source 120 indicated by (1) and(2) the output signal of the detection electrode 111 indicated by (2)and denoted by the solid line have the same phase. For this reason, theoutput signal of the multiplier 131 having a frequency twice thefrequency of the AC signal indicated by (3) is obtained as denoted bythe solid line, and the output signal of the LPF 132 in the form of a DCsignal indicated by (4) is obtained as denoted by the solid line.

In contrast, when the phase adjustment circuit 140 does not performphase adjustment, the phases of the AC signal of the AC signal source120 indicated by (1) and the output signal of the detection electrode111 indicated by (2) and denoted by the dashed line are not the same.For this reason, the DC level of the output signal of the multiplier 131is decreased as indicated by (3) and denoted by the dashed line, and theoutput signal of the LPF 132 indicated by (4) and denoted by the dashedline is a DC signal having a signal level lower than that of the DCsignal denoted by the solid line.

As described above, the phase of the AC signal input to the activeshield electrode 112 is advanced by the amount of the phase delay thatoccurs in the sensor unit 110 using the phase adjustment circuit 140 inadvance and, thus, the output signal of the detection electrode 111 canbe in phase with the AC signal output from the AC signal source 120.Therefore, the signal level of the output signal of the detectioncircuit 130 is maximized as a signal obtained by multiplying the outputsignal of the detection electrode 111 by the AC signal output from theAC signal source 120 and passing the resultant signal through the LPF132. This means maximizing the amount of change in the capacitor CH dueto the presence or absence of a detection target, such as a finger.

Therefore, it is possible to provide a capacitance detection device 100and a capacitance detection method capable of reducing a decrease in thedetection sensitivity due to the phase delay of a signal. In addition,by reducing a decrease in detection sensitivity, it is possible toprovide the capacitance detection device 100 and the capacitancedetection method capable of improving the dynamic range in detection.For example, even when a conductive film, such as an ITO film having aresistance value, is used for the detection electrode 111 or the activeshield electrode 112, the phase of the AC signal output from the ACsignal source 120 can be advanced by using the phase adjustment circuit140 and, thereafter, the AC signal can be input the active shieldelectrode 112. Thus, a decrease in the detection sensitivity of thedetection circuit 130 can be reduced.

In addition, advancing the phase of the AC signal by using the phaseadjustment circuit 140 so that the output signal of the detectionelectrode 111 and the AC signal of the AC signal source 120 are the samemeans advancing the phase of the AC signal so that the output signal ofthe detection electrode 111 and the AC signal are in phase. If the phaseof the AC signal is adjusted by the phase adjustment circuit 140, thedetection sensitivity of the detection circuit 130 can be improved evenwhen the output signal of the detection electrode 111 and the AC signalof the AC signal source 120 are completely the same, as compared withthe case where the phase of the AC signal is not adjusted by the phaseadjustment circuit 140. Therefore, if the phase of the AC signal isappropriately advanced by the phase adjustment circuit 140, a decreasein detection sensitivity of the detection circuit 130 can be reducedeven when the output signal of the detection electrode 111 and the ACsignal of the AC signal source 120 do not completely the same.

Strictly speaking, the phase of the AC signal cannot be advanced.However, the phase adjustment circuit 140 includes the phase shiftcircuit 140A that delays the phase of an AC signal and the invertingamplifier circuit 140B that inverts the phase of the AC signal. For thisreason, the phase of an AC signal can be substantially advanced, and thephase delay that occurs in the sensor unit 110 can be canceled out.

In addition, since the detection circuit 130 includes the multiplier 131and the LPF 132, the capacitance between the detection electrode 111 anda physical object, such as the hand H, can be detected using thedetection circuit 130 having a simplified configuration.

In the above description, the sensor unit 110 includes 12 detectionelectrodes 111. However, the sensor unit 110 is required to include oneor more (one or a plurality of) detection electrodes 111. Any number ofelectrodes 111 can be included.

In addition, while the above embodiment has been described withreference to the detection circuit 130 including the multiplier 131 andthe LPF 132, the detection circuit 130 may have a configuration in whichthe multiplier 131 is replaced by a differential amplifier. FIG. 7illustrates a differential amplifier 135. The differential amplifier 135includes an operational amplifier 133, resistors R1 to R4, inputterminals 135A and 135B, and an output terminal 135C. The inputterminals 135A and 135B and the output terminal 135C of the differentialamplifier 135 can be connected instead of the two input terminals andthe output terminal of the multiplier 131. That is, the differentialamplifier 135 amplifies and outputs the voltage difference between theinverting input terminal 135B connected to the detection electrode 111and the non-inverting input terminal 135A to which the AC signal isapplied. The differential amplifier 135 amplifies the difference betweenthe signals VIN+ and VIN− input to the two input terminals and outputsthe difference from the output terminal. When the output of thedifferential amplifier 135 is input to the LPF 132, an output signalsimilar to that of the detection circuit 130 including the multiplier131 and the LPF 132 is obtained. Therefore, it is possible to reduce adecrease in detection sensitivity of a detection circuit including adifferential amplifier. Moreover, the detection circuit 130 can set anintegrator circuit using an operational amplifier between the inputterminal 130A and the multiplier 131.

In addition, as illustrated in FIG. 8 , a configuration including amultiplexer (MUX) 150 may be employed. In this case, a plurality ofdetection electrodes 111 are provided. FIG. 8 illustrates a capacitancedetection device 100M according to a modification of the embodiment. Thecapacitance detection device 100M has a configuration including amultiplexer 150 on the output side of the sensor unit 110 and adetection circuit 130M instead of the detection circuit 130. Themultiplexer 150 corresponds to a selection unit and selects one or aplurality of detection electrodes 111 out of the plurality of detectionelectrodes 111 in a time division manner. Furthermore, the detectioncircuit 130M detects the capacitance between a physical object in closevicinity of the detection electrode 111 and the detection electrode 111on the basis of the detection signal output from the detection electrode111 selected by the multiplexer 150 (the selection unit) and the ACsignal output from the AC signal source 120. The phase adjustmentcircuit 140 adjusts the phase lead amount of an AC signal in accordancewith the one or plurality of detection electrodes 111 selected by themultiplexer 150.

The multiplexer 150 is provided between the sensor unit 110 and thedetection circuit 130M, divides the 12 detection electrodes 111 intofour groups G1 to G4 in the X direction, acquires the output signals ina time division manner, and outputs the output signals to the detectioncircuit 130M. Since the three detection electrodes 111 included in groupG1 are closest to the multiplexer 150, the interconnection wire lengthto the multiplexer 150 is the shortest and, thus, the resistance of theinterconnection wire is the lowest among the groups G1 to G4. The threedetection electrodes 111 included in the group G4 are the farthest fromthe multiplexer 150 and therefore have the longest interconnection wirelength to the multiplexer 150. Thus, the three detection electrodes 111have the highest wire resistance among the groups G1 to G4. When thedifference in the time constant due to the difference in interconnectionwire length has a large impact on the detection result of thecapacitance detection device 100M as the phase difference output fromthe detection electrode 111, the configuration of the capacitancedetection device 100M is effective.

The detection circuit 130M detects the capacitance between the threedetection electrodes 111 and the physical object, such as the hand H, onthe basis of the output signals of the three detection electrodes 111included in each of the groups G1 to G4 and the AC signal output fromthe AC signal source 120 in a time division manner. Therefore, thedetection circuit 130M is required to have three multipliers 131 andthree LPFs 132.

FIGS. 9A to 9C illustrate the signal waveform of each element of thecapacitance detection device 100M. “(A)” represents the AC signal of theAC signal source 120, “(B)” represents the output signal of thedetection electrodes 111 included in the group G1 when the phaseadjustment amount in the phase adjustment circuit 140 is 0 degrees, and“(C)” represents the output signals of the detection electrodes 111included in the group G4 when the phase adjustment amount in the phaseadjustment circuit 140 is 0 degrees. When one compares the group G1 withthe group G4, the phase delay α1 degrees of the output signal of thedetection electrode 111 in the group G1, which is closer to themultiplexer 150 and has a shorter interconnection wire length, is lessthan the phase delay α4 degrees of the output signal of the detectionelectrode 111 in the group G4. This is because the time constantdecreases with decreasing interconnection wire length.

FIG. 10 is a diagram describing the phase adjustment amounts in thephase adjustment circuit 140 of the capacitance detection device 100M.FIG. 10 illustrates groups G1 to G4 to be detected, phase adjustmentamounts α1 to α4, and time segments T1 to T4. The time period fordetecting the groups G1 to G4 is divided into T1 to T4 (time segments).In the time segments T1 to T4, the phase adjustment circuit 140 canadvance the phase of the AC signal input from the AC signal source 120by the phase adjustment amounts of α1 degrees to α4 degrees,respectively. In this way, by using the phase adjustment amounts of α1degrees to α4 degrees each corresponding to the interconnection wirelength of one of the groups, the output signal output from the detectionelectrode 111 in each of the groups G1 to G4 can be matched with the ACsignal output from the AC signal source 120 in the detection circuit130M, and the capacitance between the detection electrode 111 and aphysical object, such as the hand H, can be detected.

Therefore, it is possible to provide the capacitance detection device100M and the capacitance detection method capable of reducing a decreasein the detection sensitivity due to the phase delay of a signal. Inparticular, when the difference in the phase of the output signal due tothe difference in interconnection wire length between the plurality ofdetection electrodes 111 has an impact on the detection result, it isvery effective to detect the capacitance in a time division manner usingthe multiplexer 150 and to set a phase adjustment amount for each group.According to the capacitance detection device 100M, the highest signallevel of the output signal of the detection circuit 130M is obtained asa signal obtained by multiplying the output signal of the detectionelectrode 111 by the AC signal output from the AC signal source 120 andpassing the resultant signal through the LPF 132 for each group.

While the capacitance detection device and the capacitance detectionmethod according to the exemplary embodiment of the present inventionhave been described above, the present invention is not limited to thespecifically disclosed embodiment, and various changes and modificationscan be made without departing from the scope of the claims.

1. A capacitance detection device comprising: at least one detectionelectrode configured to output a detection signal associated with acapacitance formed between the detection electrode and an object inproximity of the detection electrode; an AC signal source configured tooutput an AC signal; a shield electrode disposed in a vicinity of thedetection electrode, the shield electrode being configured to receivethe AC signal; a detection circuit configured to detect the capacitancebetween the object and the detection electrode based the detectionsignal received from the detection electrode and the AC signal receivedfrom the AC signal source; and a phase adjustment circuit providedbetween the AC signal source and the shield electrode, the phaseadjustment circuit being configured to supply the AC signal to theshield electrode by advancing a phase of the AC signal output from theAC signal source.
 2. The capacitance detection device according to claim1, wherein the phase adjustment circuit advances the phase of the ACsuch that the detection signal and the AC signal input to the detectioncircuit are in phase.
 3. The capacitance detection device according toclaim 1, wherein the phase adjustment circuit includes: a phase shiftcircuit configured to delay the phase of the AC signal; and an invertingamplifier configured to invert the phase of the AC signal.
 4. Thecapacitance detection device according to claim 1, wherein the detectioncircuit includes: a multiplier configured to multiply the detectionsignal by the AC signal received from the AC signal source, therebyoutputting a multiplied signal.
 5. The capacitance detection deviceaccording to claim 4, wherein the detection circuit further includes: alow pass filter configured to block a frequency band component of themultiplied signal higher than a cutoff frequency.
 6. The capacitancedetection device according to claim 1, wherein the detection circuitincludes: an operational amplifier having an inverting input terminalconnected to the detection electrode, and a non-inverting input terminalconnected to the AC signal source, the operational amplifier beingconfigured to amplify and output a voltage difference between theinverting input and the non-inverting terminal.
 7. The capacitancedetection device according to claim 1, wherein the at least onedetection electrode includes a plurality of detection electrodes, thecapacitance detection device further comprising: a selection unitconfigured to select at least one detection electrode from among theplurality of detection electrodes in a time division manner, wherein thedetection circuit is configured to detect the capacitance between theobject and the detection electrode based on the detection signal outputfrom the at least one detection electrode selected by the selection unitand the AC signal received from the AC signal source, and wherein thephase adjustment circuit is configured to adjust an amount of phase leadin the AC signal with respect to the at least one detection electrodeselected by the selection unit.
 8. A capacitance detection method usinga capacitance detection device including at least one detectionelectrode and a shield electrode disposed in a vicinity of the detectionelectrode, the method comprising: outputting an AC signal from an ACsignal source; supplying the AC signal to the shield electrode;outputting, from the detection electrode, a detection signal associatedwith a capacitance formed between the detection electrode and an objectin proximity of the detection electrode; and detecting the capacitancebetween the object and the detection electrode based on the detectionsignal received from the detection electrode and the AC signal receivedfrom the AC signal source, wherein the supplying the AC signal to theshield electrode includes: advancing a phase of the AC signal outputfrom the AC signal source before supplying to the shield electrode. 9.The capacitance detection device according to claim 1, wherein thedetection signal includes: a detection component corresponding to thecapacitance between the detection electrode and the object; and an ACcomponent corresponding to the AC signal supplied to the shieldelectrode.
 10. The capacitance detection method according to claim 8,wherein the detection signal includes: a detection componentcorresponding to the capacitance between the detection electrode and theobject; and an AC component corresponding to the AC signal supplied tothe shield electrode.
 11. The capacitance detection method according toclaim 8, wherein the advancing the phase including: adjusting the phaseof the AC signal such that the detection signal output from thedetection electrode and the AC signal input to the detection circuit arein phase.